COVERAGE-HOLE DETECTION and SELF HEALING

ABSTRACT

A system, apparatus and techniques for detecting and self-healing coverage hole conditions in a wireless network are disclosed. The apparatus includes a monitor module that is configured in a data forwarding plane of a network switch and a regulatory module configured in a control plane of the switch. The monitor module is configured to detect a coverage hole condition affecting a mobile device associated with an access port and the regulatory module is configured to adjust transmission power to the access port based on the condition.

TECHNICAL FIELD

This disclosure relates to wireless networks and, more particularly tocoverage hole detection and self-healing in wireless networks.

BACKGROUND

In a wireless network, there can be one or more areas where the signalstrength provided to network devices is poor. These areas, commonlyknown as coverage holes, can reduce packet transfer rates from wirelessmobile units (MU) as well as limit or prohibit network access towireless mobile units. Possible causes for such coverage holes caninclude inadequate or imperfect site planning, as well as environmentalfactors that can affect the effective transmission of electromagneticsignals.

In some instances, it can be difficult to determine whether a MU is in acoverage hole as the signal received by an MU is typically not reportedback to the AP. In addition, it would be a burden to request each of thevarious MU manufactures to communicate this signal information back tothe AP using a universally agreed upon protocol. Furthermore, it isdifficult to regulate the power of access ports such that it is notexcessive. For example, when a MU moves out of a coverage hole, it canbe inefficient for an AP to maintain an increased power level.

Accordingly, there is a need for an improved approach to coverage holedetection and self-healing in wireless networks.

SUMMARY

A system, apparatus and techniques for detecting and self-healingcoverage hole conditions in a wireless network are disclosed. Theapparatus includes a monitor module that is configured in a dataforwarding plane of a network switch and a regulatory module configuredin a control plane of the switch. The monitor module is configured todetect a coverage hole condition affecting a mobile device associatedwith an access port and the regulatory module is configured to adjusttransmission power to the access port based on the condition.

For example, according to one aspect, an apparatus includes a monitormodule configured in a data forwarding plane of a network switch. Themonitor module is configured to detect a coverage hole conditionaffecting a mobile device associated with an access port. The switchalso includes a regulatory module configured in a control plane of thenetwork switch. The regulatory module is configured to adjust atransmission power to the access port in response to detection of thecoverage hole condition.

In one embodiment, the monitor module calculates transmission throughputof the access port. The monitor module can calculate the transmissionthroughput by multiplying a number of data bytes transmitted by theaccess port by a data rate for each of the number of data bytestransmitted, and summing each of the multiplied numbers.

The monitor module also can compare the transmission throughput to atarget throughput associated with the access port and detect thecoverage hole condition based on the comparison. The target throughputcan be based on an 802.11 specification. The monitor module also canmaintain a transmission data byte counter for the mobile device.

In an embodiment, the regulatory module determines the transmissionpower adjustment by determining a signal sensitivity difference betweenthe transmission throughput and a target throughput of the access portusing a sensitivity data store. The sensitivity data store includes aplurality of bit rates with associated signal sensitivities for each ofthe plurality of bit rates. The regulatory module also can store thetransmission power adjustment in a radio structure of the switch.

In one embodiment, the regulatory module adjusts the transmission powerafter a delayed time interval. The regulatory module can adjust thetransmission power in power increments.

In another aspect, a method includes monitoring transmission throughputof an access port associated with a mobile device from a data forwardingplane of a network switch, and detecting a coverage hole conditionaffecting the mobile device based on the monitoring. The method alsoincludes adjusting a transmission power to the access port from acontrol plane of the network switch in response to detection of thecoverage hole condition.

In one embodiment, the method includes calculating a transmissionthroughput of the access port. Calculating the transmission throughputcan include multiplying a number of data bytes transmitted by the accessport by a data rate for each of the number of data bytes transmitted,and summing each of the multiplied numbers.

In an embodiment, the method includes comparing the transmissionthroughput to a target throughput associated with the access port, anddetecting the coverage hole condition based on the comparison.

In one embodiment, determining the transmission power adjustmentincludes determining a signal sensitivity difference between thetransmission throughput and a target throughput of the access port usinga sensitivity data store. The sensitivity data store includes aplurality of bit rates and a signal sensitivity associated with each ofthe plurality of bit rates.

The method can also include storing the transmission power adjustment ina radio structure of the switch. The method can also include adjustingthe transmission power after a delayed time interval. For example, themethod can include adjusting the transmission power in increments.

Several advantages can be obtained using the present invention. Forexample, consider the situation in which a user performs an inventoryfunction in a warehouse using a handheld scanner. The user may walk isleby isle and enter a coverage hole caused by some temporary shelf change.Once the coverage hole condition is detected, the system can be used torespond quickly by increasing the power provided to the scanner, thusminimizing the effect of the hole on the scanner.

Additional features and advantages will be readily apparent from thefollowing detailed description, the accompanying drawings and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a system for detecting and self-healing acoverage hole in a wireless network according to the present invention.

FIG. 2 is a flow chart of example steps executed by a monitor moduleaccording to the present invention.

FIG. 3 is a flow chart of example steps executed by a regulatory moduleaccording to the present invention.

FIG. 4 illustrate data values stored in a sensitivity data storeaccording to the present invention.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 is a schematic representation of a computer network 10 configuredin accordance with an example embodiment of the invention. In thisexample, computer network 10 is configured as a WLAN. Computer network10 generally includes wireless mobile units identified by referencenumbers 18A-E, a plurality of wireless switches 14A-B, a network switch12, and a wireless access device 16. Computer network 10 may include orcommunicate with any number of additional network components, such as atraditional local area network (“LAN’). A practical embodiment can haveany number of wireless switches, each supporting any number of wirelessaccess devices, and each wireless access device supporting any number ofwireless mobile units. Indeed, the topology and configuration ofcomputer network 10 can vary to suit the needs of the particularapplication and FIG. 1 is not intended to limit the application or scopeof the invention in any way.

The wireless access device 16 is a wireless access port, which is a“thin” device that relies on network intelligence and managementfunctions provided by the network switch 12. The wireless access port 16as described herein is configured to receive data from the mobile units18A-E over wireless links. Once data is captured by the wireless accessdevice, the data is processed for communication within computer network10. For example, the data can be encapsulated into a packet formatcompliant with a suitable data communication protocol. In the exampleembodiment, data is routed within computer network 10 using conventionalEthernet 802.3 addressing (including standard Ethernet destination andsource packet addresses). In alternate embodiments, data can be routedwithin computer network 10 using conventional Internet Protocol (“IP”)techniques. In one embodiment, the wireless access port 16 stores thenumber of data bytes transmitted from each of the mobile units 18A-E.

As shown in FIG. 1, in one embodiment, the network switch 12 can be anEthernet switch, which is in turn operationally coupled to the wirelessaccess device 16. In practice, the wireless switches 14A-B cancommunicate with the wireless access device 16 via the network switch12. The wireless mobile units 18A-E are wireless devices that canphysically move around computer network 10 and communicate with networkcomponents via the wireless access device 16. Examples of mobile unitsinclude, but are not limited to, cellular phones, smart phones, personaldigital assistants (PDA), and laptop computers.

The network switch 12 is configured to include a data forwarding plane20, a control plane 24, a sensitivity data store 30, and one or moreradios 28A-B. The radios 28A-B included in the switch 12 can operate atone or more frequencies. For example, in one embodiment, one of theradios operates on a 2.4 Ghz.frequency and the other radio operates on a5 Ghz. frequency. Of course, it will be appreciated by one skilled inthe art that the number of radios included in the switch 12 of FIG. 1 isnot intended to limit the application or scope of the invention in anyway.

The data forwarding plane 20 of the switch 12 determines how to routedata packets arriving on an inbound interface of the switch 12. As shownin FIG. 1, in one embodiment, the data forwarding plane of the switch isconfigured to include a monitor module 22 that can detect coverage holeconditions in the network 10. In one embodiment, the monitor module is astateless monitor. Details of the monitor module 22 are discussed inconnection with FIG. 2.

The control plane 24 manages operational aspects of the switch 12,except the per-packet analysis and delivery of data packets arriving onan inbound interface of the switch 12, and configuration aspects of thewireless access device 16. As shown in FIG. 1, in one embodiment, thecontrol plane 24 includes a regulatory module 26 that is configured toadjust transmission power to the wireless access device 16 in responseto detection of a coverage hole condition. Details of the regulatorymodule are discussed in connection with FIG. 3.

Referring to FIG. 4, the sensitivity datastore 30 provides bit rate andassociated signal sensitivity information to both the monitor module 22and the regulatory module 26. The bit rate and signal sensitivityinformation can be derived from the IEEE 802.11 specification. Forexample, in the embodiment shown in FIG. 4, the bit rate is specified inmega-bits per second (Mbps) and the associated signal sensitivity isspecified in dBm representing the power ratio in decibels of measuredpower referenced to one milliwatt (mW). Accordingly, for any given802.11 compliant mobile unit, the mobile unit preferably sustains thebit rate at the left column 60 given the signal strength provided by thewireless access device 16 by the right column 62. For example, a givenMU preferably can sustain 18 Mbps when the supplied signal strength fromthe access device 16 is −77 dBm. Of course, it is possible that a mobileunit can achieve a higher rate than specified by the IEEE 802.11standard.

In one embodiment, the sensitivity datastore 30 is a relational databasethat provides the bit rate and signal sensitivity information to varioussystem components. In another embodiment, the sensitivity datastore 30is a directory server, such as a Lightweight Directory Access Protocol(‘LDAP’) server, that provides bit rate and signal sensitivityinformation. In other embodiments, the sensitivity datastore 30 is aconfigured area in the memory of the switch 12 that provides the bitrate and signal sensitivity information. It will be appreciated by oneskilled in the art that sensitivity datastore 30 can be used to not onlyprovide bit rate and sensitivity information but may also be used tostore data.

During network planning, a site planner typically assigns a certainthroughput number in the middle range of the available rates. This rateis referred to as a coverage rate in this disclosure.

Referring now to FIG. 2, a method executed by the monitor module 22 todetect a coverage hole condition is disclosed. First, for each mobileunit associated with an access port on each radio 28A-B, a byte counterarray is established 32. Next, in one embodiment, the access port 16maintains the byte counter array per mobile unit with associated timeand periodically updates the counter with throughput information. Thebyte counter array can be maintained by a thin AP in a histogram formatand be forwarded to the monitor module 22 at fixed time intervals 34. Inanother embodiment, the data plane of the network switch maintains thebyte counter array. Next, if the number of data packets transmitted tothe mobile unit is greater than a threshold number of packets, e.g., ten(10) packets, the monitor module 22 calculates a transmission throughputfor the access port 16 by first multiplying the byte count by the datarate these bytes transmitted 36. Next, the monitor module 22 sums eachof the multiplied numbers 38. Next, the monitor module 22 multiplies atarget/coverage rate throughput associated with the access port 16 bythe total number of data bytes transmitted 40 by the access port 16. Themonitor module 22 then compares the calculated rate-weighted byte countsto the multiplied amount 42. For example, in one embodiment, the monitormodule 22 calculates the throughput as a weighted sum average of thehistogram and performs a comparison using the following operation:

Σ(delta_bytes[i]*rate [i])<target_rate*Σ(delta_total_bytes[i])

where delta_bytes[i] is the byte count sent at rate[i] from the mobileunit at a particular time interval, delta_total_bytes[i] is the totalnumber of data bytes sent from the mobile unit at the particular timeinterval, and target_rate is the coverage rate. Advantageously, byperforming the above calculations and comparison without a divisionoperation, packet forwarding operations performed by the data forwardingplane 20 are not negatively affected as division operations are timeconsuming. If the sum of the rate-weighted byte count is less than thecoverage rate multiplied by the sum of the total number of bytes, themonitor module 22 determines that a coverage hole condition exists 44.If the rate measured is above the target rate, the network 10 isoperating normally and no coverage hole exists.

Referring now to FIG. 3, a method executed by the regulatory module 26is disclosed. As shown in FIG. 3, first, in response to receivingcoverage hole detection information from the monitor module 22, theregulatory module 26 first calculates the actual throughput by dividingthe rate-weighted byte-count 38 by the total byte-count 50. For example,in one embodiment, the regulatory module 26 calculates the actualthroughput using the following operation:

Σ(delta_bytes[i]*rate [i])/(delta_total_bytes[i])

where delta_bytes[i] is the byte count sent at rate[i] from the mobileunit at a particular time interval and, delta_total_bytes is the totalnumber of data bytes sent from the mobile unit at the particular timeinterval. Note, as this operation occurs in the control plane 24, thedivision operation is not as costly as if it would be if executed in thedata forwarding plane 20.

Next, the regulatory module 26 identifies the signal sensitivity of thecalculated actual throughput 52. This can be a lookup of informationstored in the sensitivity data store 30. Next the regulatory module 26identifies the signal sensitivity of the target throughput usinginformation stored in the sensitivity datastore 54. The regulatorymodule 26 then determines a difference value between the identifiedsignal sensitivities 56 and boosts power to the access port 16 based onthe determined difference value over a time interval 58. This calculateddifference value is stored in a radio structure of the switch and can bescheduled to take effect at a particular time interval. For example,referring to FIG. 4, if the rate measured is 9 Mbs and thetarget/coverage rate is 18 Mbs, the power boost is (−77 dBm)-(−81 dBm)which equals 4 dBm. In one embodiment, the power boost is incremented in1 dBm steps. In another embodiment, the power boost is immediatelyincreased to the desired level without a delay.

In one embodiment, once the power is boosted, the mobile unit may nolonger experience a lower coverage rate. As such, the power is steppeddown at a slower rate, e.g., −1 dBm every five (5) seconds. If themobile unit remains in the coverage hole, the regulatory module 26continues to receive measurement information from the monitor module 22and thereby maintains the increased power level at a steady state.

It will be appreciated by one skilled in the art that more than onemobile unit can be affected by a coverage hole condition. As such, theboosting power calculated for each device can be different. To addressthis issue, in one embodiment, the boost power is not immediatelyapplied by the regulatory module 26 but is delayed by some amount time,e.g., a second, from the time of the first coverage hole condition. Anynewer coverage hole condition results in a re-computing of boost power.If the new recomputed boost power is greater than the previous boostpower calculation, the greater boost power overrides and is applied tothe access port 16.

Eventually, as the coverage hole problems are resolved due to mobileunits moving to a better transmission/reception area of the network 10,the power boost to the access port 16 reverts to its original valuefinishing the coverage hole self-healing action.

Various features of the system may be implemented in hardware, software,or a combination of hardware and software. For example, some features ofthe system may be implemented in computer programs executing onprogrammable computers. Each program may be implemented in a high levelprocedural or object-oriented programming language to communicate with acomputer system or other machine. Furthermore, each such computerprogram may be stored on a storage medium such as read-only-memory (ROM)readable by a general or special purpose programmable computer orprocessor, for configuring and operating the computer to perform thefunctions described above.

1. An apparatus comprising: a monitor module configured in a dataforwarding plane of a network switch, said monitor module configured todetect a coverage hole condition affecting a mobile device associatedwith an access port; and a regulatory module configured in a controlplane of said network switch, said regulatory module configured toadjust a transmission power to said access port in response to detectionof said coverage hole condition.
 2. The apparatus of claim 1, whereinsaid monitor module calculates transmission throughput of said accessport.
 3. The apparatus of claim 2, wherein said monitor modulecalculates said transmission throughput by multiplying a number of databytes transmitted by said access port by a data rate for each of saidnumber of data bytes transmitted, and summing each of said multipliednumbers.
 4. The apparatus of claim 3, wherein said monitor modulemultiplies a target throughput associated with said access port by a sumof a total number of data bytes transmitted by said access port,compares said transmission throughput to said multiplied amount, anddetects said coverage hole condition based on said comparison.
 5. Theapparatus of claim 4, wherein said target throughput is based on an802.11 specification.
 6. The apparatus of claim 3, wherein said accessport maintains a transmission data byte counter for said mobile device.7. The apparatus of claim 3, wherein said regulatory module determinessaid transmission power adjustment by determining a signal sensitivitydifference between said transmission throughput and a target throughputof said access port using a sensitivity data store, said sensitivitydata stores comprising a plurality of bit rates and a signal sensitivityassociated with each of said plurality of bit rates.
 8. The apparatus ofclaim 7, wherein said regulatory module stores said transmission poweradjustment in a radio structure of said switch.
 9. The apparatus ofclaim 8, where said regulatory module adjusts said transmission powerafter a delayed time interval.
 10. The apparatus of claim 9, whereinsaid regulatory module adjusts said transmission power in increments.11. A method comprising: monitoring transmission throughput of an accessport associated with a mobile device from a data forwarding plane of anetwork switch; detecting a coverage hole condition affecting saidmobile device based on said monitoring; and adjusting a transmissionpower to said access port from a control plane of said network switch inresponse to detection of said coverage hole condition.
 12. The method ofclaim 11, comprising calculating a transmission throughput of saidaccess port.
 13. The method of claim 12, wherein said calculatingcomprises multiplying a number of data bytes transmitted by said accessport by a data rate for each of said number of data bytes transmitted,and summing each of said multiplied numbers.
 14. The method of claim 13,comprising: multiplying a target throughput associated with said accessport by a sum of a total number of data bytes transmitted by said accessport; comparing said transmission throughput to said multiplied amount;and detecting said coverage hole condition based on said comparison. 15.The method of claim 14, wherein said target throughput is based on an802.11 specification.
 16. The method of claim 13, further comprisingmaintaining a transmission data byte counter for said mobile device. 17.The method of claim 13, wherein determining said transmission poweradjustment comprises determining a signal sensitivity difference betweensaid transmission throughput and a target throughput of said access portusing a sensitivity data store, said sensitivity data stores comprisinga plurality of bit rates and a signal sensitivity associated with eachof said plurality of bit rates.
 18. The method of claim 17, comprisingstoring said transmission power adjustment in a radio structure of saidswitch. 19 The method of claim 18, comprising adjusting saidtransmission power after a delayed time interval.
 20. The method ofclaim 19, comprising adjusting said transmission power in increments.21. A network system comprising: an access port providing communicatingwith at least one mobile device; and a network switch in communicationwith said access port, said network switch including a monitor moduleconfigured in a data forwarding plane of a network switch, said monitormodule configured to detect a coverage hole condition affecting a mobiledevice associated with an access port, and a regulatory moduleconfigured in a control plane of said network switch, said regulatorymodule configured to adjust a transmission power to said access port inresponse to detection of said coverage hole condition.